Fire extinguishing systems

ABSTRACT

A fire extinguishing system is disclosed comprising several self-contained extinguishers. Each includes a thermallyrupturable bulb for releasing the extinguishant in response to detection of incipient fire conditions in the neighborhood of that extinguisher, electrically operated discharge means also capable of releasing the extinguishant, and one or more electrical switches operated in response to discharge of the extinguishant. In the system, the electrical switches of all the extinguishers are interconnected with the electrically operated discharge means of all the extinguishers so that operation of any one of the extinguishers by rupture of its bulb causes operation of each other extinguisher in the system.

[ 1' FIRE EXTINGUISHING SYSTEMS [75] Inventor: Alister L. McCulloch, Moorabbin,

Victoria, Australia [73] Assignee: Graviner (Colnbrook) Limited,

London, England 22 Filed: July13, 1972 21 Appl. No.: 271,590

[30] Foreign Application Priority Data [451 May 21, 1974 Mathis 169/26 Job 169/41 X Primary Examiner-M. Henson Wood, Jr.

Assistant Examiner-Michael Mar 7 Attorney, Agent, or Firm-Wolfe, Hubbard, Leydig, Voit & Osann, Ltd.

[5 7] ABSTRACT A fire extinguishing system is disclosed comprising several self-contained extinguishers. Each includes a thermally-rupturable bulb for releasing the extinguishant in response to detection of incipient fire conditions in the neighborhood of that'extinguisher, electrically operated discharge means also capable of releasing the extinguishant, and one or more electrical switches operated in response to discharge of the extinguishant. In the system, the electrical switches of all the extinguishers are interconnected with the electrically operated discharge means of all the extinguishers so that operation of any one of the extinguishers by rupture of its bulb causes operation of each other extinguisher in the system.

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1 FIRE EXTINGUISHING SYSTEMS The invention relates to fire extinguishing systems, and more particularly to automatically operated fire extinguishers and fire extinguishing systems.

According to the invention, there is provided afire extinguisher, including a normally closed extinguishant discharge opening, first control means operative in response to incipient fire conditions in the neighbourhood of the extinguisher to open the discharge opening if closed, second control means operative in response to an electrical signal to open the discharge opening if closed, and electrical signalling means responsive to discharge of the'extinguishant.

According to the invention, there is also provided a fire extinguishing system, comprising at least two selfcontained extinguishers each of which includes a container for holding extinguishant under pressure, a normally closed extinguishant discharge opening, means responsive to incipient fire conditions in the neighborhood of that extinguisher for opening its discharge opening, electrically responsive discharge means also capable of opening the discharge opening, and electrical signalling means for generating an electrical signal in response to opening of the discharge opening of that extinguisher, the system also including electrical circuitry interconnecting the electrical signalling means and the electrically responsive discharge means of the extinguishers whereby generation of said electrical signal by any one extinguishers electrical signalling means causes the electrically responsive discharge means of each other extinguisher to open its discharge opening.

Automatic fire extinguishers and automatic fire extinguishing systems embodying the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

FIG. 1 is a general side elevation of one of the automatic fire extinguishers,

FIG. 2 is a part cross-section, part side elevation, of the extinguisher of FlG.l;

FIG. 3 is a circuit diagram of circuitry for use in a system incorporating several extinguishers of the type shown in FIGS. 1 and 2;

FIG. 4 shows a modification to part of the fire extinguisher of FIGS. 1 and 2;

FIG. 5 is a part cross-section, part side elevation, of another of the fire extinguishers;

FIG. 6 is an underside view of the extinguisher of FIG. 5;

FIG. 7 is a section of part of the extinguisher of FIGS. 5 and 6, taken on the line VII-VII of FIG. 6; and

FIG. 8 is a cross-section corresponding to FIG. 7 but taken on the line VIIIVIII of FIG. 6.

The extinguisher shown in FIGS. 1 and 2 comprises a rechargeable container 10 containing the extinguishant (which may be a chemical. extinguishant such as bromochlorodifluoromethane) which is suspended by a bracket 14 from the roof 12 in the area to be protected, through the intermediary of a weight-sensitive switch 16. At its lower end, the container 10 carries a sprinkler head 18. When activated in a manner to be described, the sprinkler head 18 opens a valve in a valve head 20, whereupon the extinguishant exits under pressure into the area to be protected.

The weight sensitive switch 16 is arranged to produce an electrical output when the weight of the extinguisher changes as a result of loss of the extinguishant. It comprises a tubular member 20 which is screw-mounted to the bracket 14 through the intermediary of a tube 22. A contact boss, made of electrically insulating material and supporting electrical contacts 26 and 28, is secured within the member 20. A plunger 30 is attached to the top of the container 10 and is slidable within the member 20. The plunger 30 has an electrically conductive head 32, and a compression spring 34 acts between the underside of this head and an inwardly directed annular flange at the bottom of the tubular member 20. The spring rate is such that the container 10, when full of extinguishant, has sufficient weight to compress the spring and to create a gap between the contacts 26, 28 and the plunger head 32. When the container 10 is at least partially empty (due to use or leakage), the force exerted by the spring 34 is able to lift the plunger 30 so upper end of the bulb 44 closes off a valve in the valve head 20. The adjustable screw enables the position of the bulb 44 to be set so as to hold the valve closed.

The valve 44 is filled with a thermally sensitive fluid which expands rapidly when its temperature rises.

In addition, the bracket 40 supports an explosive actuator 46. The actuator includes a hollow chamber 50 which is closed off by a removable plug 52 and from which a narrow hollow tubular extension 54 leads. A plunger 56 is slidable in the bore of the extension 54 and, when fully extended, strikes the bulb 44. The head of the plunger 56 is slidable within the hollow chamber 50 in which is situated an explosive charge 58. The plug 52 carries an electrically responsive detonator, connections to which are made by a cable 60.

The bracket 40 also supports a microswitch 61 which has a spring-loaded plunger engaging the glass bulb 44. The contacts of the microswitch 61 are connected to a cable 62.

The extinguishant container 10 carries a pressuresensitive switch 64 which senses the pressure of the extinguishant in the container and closes a pair of ers are electrically connected together by means of the power supply and control circuit shown in FIG. 3.

In FIG. 3, it is assumed (for the purposes of example) that there are three extinguishers in the system. FIG. 3 shows the cables 36, 62 and 66 leading respectively from the weight-sensitive switch 16, the microswitch 61 and the pressure-sensitive switch 64 of the first extinguisher in the system. These cables are connected to an input unit 67. This energizes a line 68 with a binary 1 when cable 36 is bridge by the contacts of the weight sensitive switch 16, energizes a line 69 with a binary 1 when cable 62 is bridged by the contacts of the microswitch 61, and energizes a line 70 with a binary 1 when cable 66 is bridged by the contacts of the pressure-sensitive switch 64. Lines 68, 69 and 70 are connected to AND gates 71 and 72 and to an OR gate 73 in the manner indicated.

In operation, operation of either the weight-sensitive switch 16 or the pressure-sensitive switch 64 activates the OR gate 73 and the latter in turn activates a warning unit 74. This indicates that there has been a. loss of extinguishant from the extinguisher as by leakage or use.

An abnormal rise in ambient temperature in part of the area protected by the extinguishers causes the fluid in the glass bulb 44 of the extinguisher in that part of the area to expand and rupture the bulb. This releases the valve in the valve head 20 and the extinguishant is sprayed into the area through the sprinkler head 18, under the pressure in the container 10. Simultaneously, the plunger of the microswitch 61 is released by the shattered bulb, and closes the microswitch contacts to bridge the cable 62. The release of the extinguishant also rapidly reduces the weight of the container 10, and the plunger 32 in the weight-sensitive switch 16 therefore rises under the action of the spring 34 until it electrically bridges the contacts 26 and 28. At the same time, the release of the extinguishant lowers the pres sure in the container 10, and the contacts of the switch sensitive switch 64 has operated, provided the microswitch 61 has also operated.

The circuit of FIG. 3 includes similar items for the other two extinguishers of the system and these are similarly referenced save for the distinguishing suffixes A and B.

Lines 75, 75A and 75B are connected to an OR gate 77 which controls an output unit 78 feeding the cables 60 of the three extinguishers. Whenever any one (or more) of the three output lines 75, 75A and 75B is energised (indicating that one extinguisher has operated), the OR gate 77 causes the output unit 78 to energise the three cables 66. Therefore, the explosive actuators 46 of all three extinguishers are'detonated and their plungers 56 shatter their glass bulbs 44 (except the glass bulb of the first extinguisher which has of course already been shattered by the local rise in ambient temperature). In this way, automatic operation of any one of the extinguishers in response to a local rise in ambient temperature automatically causes operation of all the other extinguishers protecting that area, and the whole area is, almost instantaneously, saturated with extinguishant fluid.

The circuit of FIG. 3 may be provided with a smoke detector 79 to detect incipient fire conditions in the general neighbourhood of all the extinguishers, and this is connected to fire all the extinguishers via the or gate If desired, one of the switches 16 and 64 may be'dispensed with in each extinguisher. In such a case the other switch alone would control the warning unit 74 and, using a single AND gate instead of the two gates 71 and 72, would control the output line 75 in combination with the microswitch 6].

FIG. 4 shows a modification to the sprinkler head 18 of the extinguisher of FIGS. 1 and 2, and parts in FIG. 4 corresponding to parts in FIGS. 1 and 2 are similarly referenced. As shown in FIG. 4, the bracket 40 is not provided with the explosive actuator 46, but instead the glass bulb 44 carries, at its lower end, an electrically detonatable explosive charge having electric leads connected to the cable 60.

The operation is generally the same as described above with reference-to FIGS. 1 to 3. When one extinguisher is set off by rupture of its glass bulb 44 owing to abnormal temperature rise, the resultant electrical signal produced by its microswitch 61, in combination with the weight-sensitive switch 16 and pressuresensitive switch 64, cause energisation of the cables 60 of all the extinguishers, and the detonatable charges 80 are set off to rupture the glass bulbs 44 of the other extinguishers in the system so that, as before, all extinguishers are set off.

In a further modification, the detonatablecharge 80 of FIG. 4 is removed, and instead the bulb 44 is associated with an electrically'energisable heater which is energised from the cable 60 in the event of actuation of the system. The heat generated by the heater ruptures the bulb 44. i

The extinguisher shown in FIGS. 1 and 2 may be arranged to discharge its contents (30 lbs. of extinguishant, for example) in about 4 seconds, and the remaining extinguishers in the-system can be actuated and discharge their contents within 10 seconds.

FIGS. 5 to 8 show another extinguisher embodying the invention, and items in these Figures corresponding to items in FIGS. 1 and 2 are similarly referenced.

As before, the extinguisher of FIGS. 5 to 8 is roofsupported by means of a weight-sensitive switch 16.

The switch 16 is held in position on the bracket 14 by quick-release catches 90, and the bracket 14 is itself fixed to a base plate 91 and to the roof.

The switch 16 comprises an outer tubular member 20, engaged by the catches 90, into which slidably extends the plunger 30 fast with the extinguishant container 10. The plunger 30 is hollow but incorporates a closingoff plug 98. A microswitch is fixed to the base plate 91 of the extinguisher and extends into the hollow plunger 30. When the extinguisher has operated and discharged its extinguishant, the spring 34 can lift the plunger 30 into the position illustrated, and the plug 98 then strikes the actuator 102 of the microswitch and closes its contacts.

A cover 104 is provided to clip onto the base plate 91, and this cover is apertured to accommodate the sprinkler head 18. I v

The sprinkler head 18 comprises a hollow, generally cylindrical member 1 10 whose upper end is open to the inside of the container 10 and which is welded in position on the bottom of the container 10. The internal bore of the member is threaded to receive a collar 112 which clamps a circular sealing ring 114 in place.

The lower end of the collar 112 is closed off by a sealing diaphragm 116 which is supported by a circular support 1 18.

The support 118 is held in position by three balls 120, 122, and 124 which engage the charnfered edge of the support 118. The halls 120, 122 and 124 are located in the ends of radially directed bores (mutually spaced by extending through the wall of the member 110.

Each of the bores 126, 128 and 130 is internally threaded. Bore 126 threadably supports a cylindrical explosive actuator 134 which is closed off by a removable plug 136 and incorporates a piston 138 engaging the ball 120 When the piston 138 is in place, as illustrated in FIG. 7, it urges the piston into a position in which it presses the ball 120 into contact with the support 118. The piston 138 incorporates an explosive charge 140 and an electrically operated detonator 142. This detonator is connected by electric leads 144 to the cable 60 which is positioned in a circumferential slot 146 in the member 110. This slot is closed off by a protective 'cover 148.

The radial bore 128 supports a glass bulb 150 whichis held in position in a hollow cylinder 152 having an open end closed off by a removable plug 154. The inner end of the glass bulb 150 presses against the ball 122 and holds it in contact with the support 118. The bulb 150 is similar to the bulb 44 of the extinguisher of FIG. 1 and incorporates a heat sensitive fluid.

The radial bore 130 (FIGS) supports a plunger in a hollow cylinder 162. The cylinder 162 is closed off by a removable plug 164, and a spring 165 urges the plunger 160 into contact with the ball 124 and holds'it against the support 118. The plunger 160-has a collar 166 which is engaged by the striker arm 168 of a microswitch 170 supported on a bracket 172from the cylinder 162. The contacts of the microswitch 170 are connected to the cable 62 which is located in the slot 146.

The lower end of the member 110 is partially closed off by an apertured disc which is held in place by an apertured dome 182.

As shown in FIG. 5, cables 36 and 66are connected to a terminal block 182 and led away to the circuitry of FIG. 3, together with the cable 62. Cable 60 is connected to the explosive actuator 134 via the same terminal block.

As with the extinguisher of FIGS. 1 and 2, the area to be protected is provided with several extinguishers of the type illustrated in FIGS. 5 to 8, and their cables 66 and 68 are connected together to a circuit of the form shown in FIG. 3.

In operation, incipient fire conditions in part of the. area to be protected cause a local rise in ambient temperature, and this causes rupture of the glass bulb 150 of the extinguisher in that area. This releases the ball 122, and the resultant reduction in support for the support member 118'is sufficient to cause the member'1l8 to drop, thus releasing the sealing diaphragm 116. The. extinguishant in the container 10 therefore discharges.

When the support member 118 of the extinguisher is released in the manner described and drops, it releases the ball 124 (FIG.8) of the extinguisher, and the plunger 160 can thus move radially inwards of the sprinkler head 18 and actuate the microswitch 170. The latter therefore bridges cable 62.

As before, discharge of the extinguishant also actuates the weight-sensitive switch 16 and the pressure switch 64 (FIG. 5).

In the same manner as described above, the circuit of FIG.3 therefore energises the cables 60 of all the extin- 6 guishers. This causes the detonators 142 in the explosive actuators 134 of all the extinguishers to be set off,

thus rupturing the pistons 138 and releasing the balls 120. The support members 118 in the other extinguishers therefore drop, and release the sealing diaphragms 116 so that the other extinguishers also discharge their extinguishant.

As with the extinguishers of FIGS. 1 and 2, the extinguisher of FIGS. 5 to 8 can be modified by dispensing with one or otherof the switches 16 and 64, and appropriately modifying the circuitry.

The fire extinguisher systems described are advantageous in that they enable extinguishant to be discharged, substantially simultaneously, at a number of different points in an area to be protected, and yet require only electrical connections between the different points: pipe work from a central reservoir to each distribution point is therefore avoided. Fusible links may replace the glass bulbs to hold the discharge openings shut until fused by heat.

I claim:

1. In a fire extinguisher having a body including an extinguishant container with a normally closed extinguishant discharge opening,

a rupturable bulb containing thermally expansive fluid, means supporting the bulb adjacent to the said openmeans supported by the bulb for holding the opening closed until the bulb is ruptured by thermal expansion of the said fluid in response to incipient fire conditions in the neighborhood of the extinguisher whereupon the bulb ruptures, and opens the discharge opening,

control means mounted on the body and associated with the discharge opening and operative in response to an electrical signal to open the discharge opening if the latter is closed, and

electrical signalling means mounted on the body and responsive to discharge of the extinguishant to produce an electrical signal.

2. An extinguisher according to claim 1, in which said control means comprises electrically detonatable explosive-actuated means,

and

means mounting the explosive-actuated means adjacent the bulb so as to rupture the bulb when the explosive-actuated means is electrically detonated.

3. An extinguisher according to claim 1, in which the electrical signalling means comprises an electrical switch,

means mounting the electrical switch adjacent to the bulb, and

an operating member biased into contact with the bulb and connected to the'switch so as to operate the switch when the bulb ruptures.

4. In a fire extinguisher having a body including an extinguishant container with a normally closed extinguishant discharge opening,

control means mounted on the body and associated with the discharge opening and operative in response to incipient fire conditions in the neighborhood of the extinguisher to open the discharge opening if the latter is closed,

electrically detonatable explosive-actuated means operatively associated with the discharge opening for opening the latter when electrically detonated, and

electrical signalling means mounted on the body and responsive to discharge of the extinguishant to produce an electrical signal.

5. In a fire extinguisher having a body including an extinguishant container with a normally closed extinguishant discharge opening,

first control means mounted on the body and associated with the discharge opening and operative in response to incipient fire conditions in the neighborhood of the extinguisher to open the discharge opening if the latter is closed,

second control means mounted on the body and associated with the discharge opening and operative in response to an electrical signal to open the discharge opening if the latter is closed,

mounting means for supporting the weight of the extinguisher body and including first and second members arranged to undergo relative movement in response to a change of weight of the extinguisher following loss of extinguishant from the container thereof, and

electrical switch means fixedly mounted relative to one said member whereby to be operated by the said relative movement in response to the change in weight of the extinguisher as a result of loss of extinguishant therefrom.

6. In a fire extinguisher having a body including an extinguishant container with a normally closed extinguishant discharge opening,

first control means mounted on the body and associated with the discharge opening and operative in response to incipient fire conditions in the neighborhood of the extinguisher to open the discharge opening if the latter is closed,

second control means mounted on the body and associated with the discharge opening and operative in response to an electrical signal to open the discharge opening if the latter is closed,

first electrical switch means mounted on the extinguisher body to sense whether the discharge opening is closed or open so as to be operated when the discharge opening is opened,

second electrical switch means mounted on the extinguisher body to be susceptible to the extinguishant therein so as to be operated in response to loss of extinguishant therefrom, and

circuitry connected to the first and second switch means to produce an output only when both are operated.

7. An extinguisher according to claim 6, including mounting means for supporting the weight of the extinguisher body and having first and second members arranged to undergo relative movement in response to a change in weight of the extinguisher body, and in which the second electrical switch means comprises an electrical switch arranged to be operated in response to the said relative movement of the first and second members resulting from loss of extinguishant from the con-. tainer.

8. An extinguisher according to claim 6, in which the second electrical switch means comprises a pressuresensitive switch responsive to the pressure of the extinguishant if any in the container so as to be operated by loss of extinguishant therefrom.

9. In a fire extinguisher having a body including an extinguishant container with a normally closed extinguishant discharge opening,

a releasable diaphragm matching the said discharge opening, and first and second retaining members disposed at circumferentially spaced positions around the perimeter of the discharge opening to hold the diaphragm in a position in which it closes the said discharge opening;

a rupturable bulb mounted on the extinguisher body to locate the-first retaining member and containing thermally expansive fluid which expands in response to detection of incipient fire conditions and ruptures the bulb to cause the displacement of the first member;

locating member associated with an electrically detonatable explosive charge and mounted on the extinguisher body tolocate the second retaining member until the locating member is ruptured by detonation of the explosive charge in response to the said electrical signal and causes displacement of the second retaining member; the diaphragm being freed, to open the discharge opening, upon displacement of at least one of the first and second retaining members; and electrical signalling means mounted on the body and responsive to discharge of the extinguishant to pro duce an electrical signal. 10. An extinguisher according to claim 9, including a third retaining member disposed at the perimeter of the discharge opening at a position spaced circumferentially therearound from the first and second retaining members, and means biasing the third retaining member into the said position from which it is displaced by release of the diaphragm, and in which the electrical signalling means comprises an electrical switch and means mounting the electrical switch on the extinguisher body so that his operated in response to displacement of the third retaining member.

11. An extinguisher according to claim 10, including a circular support member having a peripheral chamfer,

means supported on the extinguisher body and defining first and second bores directed radially of the discharge opening and respectively receiving the first and second retaining members which are spherical in shape and are loosely positioned in and protrude from the ends of the bores to contact the chamfered edge of the support member whereby to hold the support member in a position in which it supports the diaphragm in the opening against the pressure of the extinguishant; the said rupturable bulb being disposed radially of the discharge opening and located to hold the first spherical member in engagement with the chamfer until the bulb is ruptured; the second locating member comprising a piston slidable in the second bore to hold the second spherical member in engagement with the chamfer and incorporating the explosive charge whereby to be ruptured by electrical detonation of the explosive charge to release the second spherical member. 12. An extinguisher according to claim 11, including means defining a third bore directed radially of the discharge opening and spaced circumferentially therearound relative to the first and second bores, and in which the third retaining member comprises a third spherical member which is loosely located in and protrudes from the third bore, and including a spring-urge member slidable in the third bore to hold the third spherical member against the said chamfer whereby to be urged radially inwards on release of the third spherical member when the support member is displaced, and in which the said electrical switch is positioned to be actuated by the radially inward movement of the spring-urged member.

13. A fire extinguishing system, comprising at least two selfcontained extinguishers each of which includes a container for holding extinguishaht under pressure, means defining a normally closed extinguishant discharge opening for discharging extinguishant from the container, means responsive to incipient fire conditions in the neighborhood of the extinguisher for opening its discharge opening, electrically responsive means capable of opening the discharge opening in response to an electrical signal independent of said incipient fire conditions, and electrical signalling means operative to generate a said electrical signal in response to opening of the discharge opening of that extinguisher, electrical circuitry interconnecting the electrical signalling means and the electrically responsive discharge means of the extinguishers whereby generation of a said electrical signal by any one extinguishers electrical signalling means causes the electrically responsive means of each other extinguisher to open its discharge opening, detector means mounted to be operative in response to incipient fire conditions in the general neighborhood of all the extinguishers to produce a further electrical signal, and circuitry responsive to this further electrical signal and connected to said electrically responsive means of each of the extinguishers to actuate them all in response to the further electrical signal. 14, A fire extinguishing system comprising at least two self-contained extinguishers each of which includes a container for holding extinguishant under pressure, means defining a normally closed extinguishant discharge opening for discharging extinguishant from the container, thermally responsive'means responsive to incipient fire conditions in the neighborhood of the extinguisher 10 for opening its discharge opening, electrically responsive means capable of opening the discharge opening in response to an electrical signal indcpen-- dent of said incipient fire conditions, first electrical switch means, means mounting the first electrical switch means to be operated in response to the opening of the discharge opening of the respective extinguisher, second electrical switch means, means responsive to loss of extinguishant from the container of the respective extinguisher to operate the second electrical switch means, and first electrical circuitry connected to the first and second electrical switch means and responsive thereto to produce an electrical signal only when both are in the operated condition at the same time, and

second electrical circuitry interconnecting the first electrical circuitry and the electrically responsive means on the extinguishers whereby generation of a said electrical signal by one extinguishers said first electrical circuitry causes the electrically responsive discharge means of each other extinguisher to open its discharge opening.

15. A system according to claim 14, including mounting means for supporting the weight of each extinguisher and including first and second members arranged to undergo relative movement in response to a change in weight of the extinguisher, and in which each second electrical switch means includes a weightresponsive electrical switch associated with the first and second members of the corresponding extinguisher so as to be operated by the said relative movement resulting from loss of extinguishant from the container of that extinguisher.

16. A system according to claim 15, in which each second electrical switch means also includes a pressure-responsive switch mounted on the container of the corresponding extinguisher to be operated in response to loss of pressure therefrom, the said electrical circuitry comprising logic means operative to produce a said electrical signal only when the first switch means is in the operated condition at the same time as at least one of the weight-responsive and pressure-responsive switches. 

1. In a fire extinguisher having a body including an extinguishant container with a normally closed extinguishant discharge opening, a rupturable bulb containing thermally expansive fluid, means supporting the bulb adjacent to the said opening, means supported by the bulb for holding the opening closed until the bulb is ruptured by thermal expansion of the said fluid in response to incipient fire conditions in the neighborhood of the extinguisher whereupon the bulb ruptures, and opens the discharge opening, control means mounted on the body and associated with the discharge opening and operative in response to an electrical signal to open the dischaRge opening if the latter is closed, and electrical signalling means mounted on the body and responsive to discharge of the extinguishant to produce an electrical signal.
 2. An extinguisher according to claim 1, in which said control means comprises electrically detonatable explosive-actuated means, and means mounting the explosive-actuated means adjacent the bulb so as to rupture the bulb when the explosive-actuated means is electrically detonated.
 3. An extinguisher according to claim 1, in which the electrical signalling means comprises an electrical switch, means mounting the electrical switch adjacent to the bulb, and an operating member biased into contact with the bulb and connected to the switch so as to operate the switch when the bulb ruptures.
 4. In a fire extinguisher having a body including an extinguishant container with a normally closed extinguishant discharge opening, control means mounted on the body and associated with the discharge opening and operative in response to incipient fire conditions in the neighborhood of the extinguisher to open the discharge opening if the latter is closed, electrically detonatable explosive-actuated means operatively associated with the discharge opening for opening the latter when electrically detonated, and electrical signalling means mounted on the body and responsive to discharge of the extinguishant to produce an electrical signal.
 5. In a fire extinguisher having a body including an extinguishant container with a normally closed extinguishant discharge opening, first control means mounted on the body and associated with the discharge opening and operative in response to incipient fire conditions in the neighborhood of the extinguisher to open the discharge opening if the latter is closed, second control means mounted on the body and associated with the discharge opening and operative in response to an electrical signal to open the discharge opening if the latter is closed, mounting means for supporting the weight of the extinguisher body and including first and second members arranged to undergo relative movement in response to a change of weight of the extinguisher following loss of extinguishant from the container thereof, and electrical switch means fixedly mounted relative to one said member whereby to be operated by the said relative movement in response to the change in weight of the extinguisher as a result of loss of extinguishant therefrom.
 6. In a fire extinguisher having a body including an extinguishant container with a normally closed extinguishant discharge opening, first control means mounted on the body and associated with the discharge opening and operative in response to incipient fire conditions in the neighborhood of the extinguisher to open the discharge opening if the latter is closed, second control means mounted on the body and associated with the discharge opening and operative in response to an electrical signal to open the discharge opening if the latter is closed, first electrical switch means mounted on the extinguisher body to sense whether the discharge opening is closed or open so as to be operated when the discharge opening is opened, second electrical switch means mounted on the extinguisher body to be susceptible to the extinguishant therein so as to be operated in response to loss of extinguishant therefrom, and circuitry connected to the first and second switch means to produce an output only when both are operated.
 7. An extinguisher according to claim 6, including mounting means for supporting the weight of the extinguisher body and having first and second members arranged to undergo relative movement in response to a change in weight of the extinguisher body, and in which the second electrical switch means comprises an electrical switch arranged to be operated in response to the said relative movement of the first and second members resulting from loss of extinguishant from the coNtainer.
 8. An extinguisher according to claim 6, in which the second electrical switch means comprises a pressure-sensitive switch responsive to the pressure of the extinguishant if any in the container so as to be operated by loss of extinguishant therefrom.
 9. In a fire extinguisher having a body including an extinguishant container with a normally closed extinguishant discharge opening, a releasable diaphragm matching the said discharge opening, and first and second retaining members disposed at circumferentially spaced positions around the perimeter of the discharge opening to hold the diaphragm in a position in which it closes the said discharge opening; a rupturable bulb mounted on the extinguisher body to locate the first retaining member and containing thermally expansive fluid which expands in response to detection of incipient fire conditions and ruptures the bulb to cause the displacement of the first member; a locating member associated with an electrically detonatable explosive charge and mounted on the extinguisher body to locate the second retaining member until the locating member is ruptured by detonation of the explosive charge in response to the said electrical signal and causes displacement of the second retaining member; the diaphragm being freed, to open the discharge opening, upon displacement of at least one of the first and second retaining members; and electrical signalling means mounted on the body and responsive to discharge of the extinguishant to produce an electrical signal.
 10. An extinguisher according to claim 9, including a third retaining member disposed at the perimeter of the discharge opening at a position spaced circumferentially therearound from the first and second retaining members, and means biasing the third retaining member into the said position from which it is displaced by release of the diaphragm, and in which the electrical signalling means comprises an electrical switch and means mounting the electrical switch on the extinguisher body so that it is operated in response to displacement of the third retaining member.
 11. An extinguisher according to claim 10, including a circular support member having a peripheral chamfer, means supported on the extinguisher body and defining first and second bores directed radially of the discharge opening and respectively receiving the first and second retaining members which are spherical in shape and are loosely positioned in and protrude from the ends of the bores to contact the chamfered edge of the support member whereby to hold the support member in a position in which it supports the diaphragm in the opening against the pressure of the extinguishant; the said rupturable bulb being disposed radially of the discharge opening and located to hold the first spherical member in engagement with the chamfer until the bulb is ruptured; the second locating member comprising a piston slidable in the second bore to hold the second spherical member in engagement with the chamfer and incorporating the explosive charge whereby to be ruptured by electrical detonation of the explosive charge to release the second spherical member.
 12. An extinguisher according to claim 11, including means defining a third bore directed radially of the discharge opening and spaced circumferentially therearound relative to the first and second bores, and in which the third retaining member comprises a third spherical member which is loosely located in and protrudes from the third bore, and including a spring-urge member slidable in the third bore to hold the third spherical member against the said chamfer whereby to be urged radially inwards on release of the third spherical member when the support member is displaced, and in which the said electrical switch is positioned to be actuated by the radially inward movement of the spring-urged member.
 13. A fire extinguishing system, comprising at least two self-contained extinguishers each of which includes a container for hOlding extinguishant under pressure, means defining a normally closed extinguishant discharge opening for discharging extinguishant from the container, means responsive to incipient fire conditions in the neighborhood of the extinguisher for opening its discharge opening, electrically responsive means capable of opening the discharge opening in response to an electrical signal independent of said incipient fire conditions, and electrical signalling means operative to generate a said electrical signal in response to opening of the discharge opening of that extinguisher, electrical circuitry interconnecting the electrical signalling means and the electrically responsive discharge means of the extinguishers whereby generation of a said electrical signal by any one extinguisher''s electrical signalling means causes the electrically responsive means of each other extinguisher to open its discharge opening, detector means mounted to be operative in response to incipient fire conditions in the general neighborhood of all the extinguishers to produce a further electrical signal, and circuitry responsive to this further electrical signal and connected to said electrically responsive means of each of the extinguishers to actuate them all in response to the further electrical signal.
 14. A fire extinguishing system comprising at least two self-contained extinguishers each of which includes a container for holding extinguishant under pressure, means defining a normally closed extinguishant discharge opening for discharging extinguishant from the container, thermally responsive means responsive to incipient fire conditions in the neighborhood of the extinguisher for opening its discharge opening, electrically responsive means capable of opening the discharge opening in response to an electrical signal independent of said incipient fire conditions, first electrical switch means, means mounting the first electrical switch means to be operated in response to the opening of the discharge opening of the respective extinguisher, second electrical switch means, means responsive to loss of extinguishant from the container of the respective extinguisher to operate the second electrical switch means, and first electrical circuitry connected to the first and second electrical switch means and responsive thereto to produce an electrical signal only when both are in the operated condition at the same time, and second electrical circuitry interconnecting the first electrical circuitry and the electrically responsive means on the extinguishers whereby generation of a said electrical signal by one extinguisher''s said first electrical circuitry causes the electrically responsive discharge means of each other extinguisher to open its discharge opening.
 15. A system according to claim 14, including mounting means for supporting the weight of each extinguisher and including first and second members arranged to undergo relative movement in response to a change in weight of the extinguisher, and in which each second electrical switch means includes a weight-responsive electrical switch associated with the first and second members of the corresponding extinguisher so as to be operated by the said relative movement resulting from loss of extinguishant from the container of that extinguisher.
 16. A system according to claim 15, in which each second electrical switch means also includes a pressure-responsive switch mounted on the container of the corresponding extinguisher to be operated in response to loss of pressure therefrom, the said electrical circuitry comprising logic means operative to produce a said electrical signal only when the first switch means is in the operated condition at the same time as at least one of the weight-responsive and pressure-responsive switches. 